Preparation, structure and electrochemical behavior of dinuclear cyclooctadiene-chelated Ir(I) complexes with 2-aminopyridinato bridges

Dinuclear iridium(I) complexes with two bridging aminopyridinato ligands, [Ir(μ-L)(COD)]2 (COD=1,5-cyclooctadiene (1): L=2-aminopyridinato (ap) (2): L=2-anilinopyridinato (anp)), were prepared from [Ir(μ-Cl)(COD)]2 and Li+L− in a 24–36% yield. These compounds were characterized by X-ray structure analysis and 1H NMR spectroscopy. Two iridium atoms were bridged by two aminopyridinato ligands and each iridium atom was coordinated by one chelating COD. The coordination sphere of each Ir(I) center, which was formed by two N atoms and two olefinic π bonds, was square planar. Ir⋯Ir separations in 1 and 2 were 3.0998(6) and 3.0681(3) Å, respectively. Cyclic voltammetry of 1 and 2 in n-Bu4NPF6/CH2Cl2 exhibited a chemically reversible oxidation wave at −0.41 and −0.36 V versus Fc+/Fc, respectively. These potentials were lower than those of [Ir(μ-form)(COD)]2 (form=anion of N,N′-di-p-tolylformamidine), [Ir(μ-hp)(COD)]2 (hp=anion of 2-hydroxypyridine), [Ir(μ-mhp)(COD)]2 (mhp=anion of 6-methyl-2-hydroxypyridine) and [Ir(μ-pz)(COD)]2 (pz=anion of pyrazole). Electrolytic one-electron oxidation of 2 gave its stable cationic radical, [Ir(μ-anp)(COD)]2 +, of which frozen solution ESR spectrum was rhombic with g1=2.43, g2=2.30 and g3=2.08 and no hyperfine splitting was resolved.